This invention relates, in general, to particle beam accelerators and, more specifically, to RF amplifier configurations for creating electric fields within a resonant cavity.
Particle beam accelerators require large amounts of RF energy to produce the accelerating fields in cavity structures, such as drift tube linacs and radio frequency quadrapoles. The RF requirements range from a few kilowatts up to several megawatts, at all duty cycles up to continuous wave (CW). The majority of the prior art particle beam accelerators have used klystron amplifiers to provide the high power RF energy to the resonant cavity, but solid state amplifiers are becoming more popular and offer the greatest promise for increased reliability, efficiency, and ease of operation.
Various solid state amplifier arrangements have been proposed for use in particle beam accelerators. For example, U.S. Pat. No. 4,064,464, issued Dec. 20, 1977 to the same inventor and assignee as the present invention, discloses a solid state amplifier which may be used to provide the high power necessary to drive the cavity in a particle beam accelerator. The referenced patent includes a phase control system which regulates the amount of power provided at the output of the amplifier system. Such system is advantageous over prior art systems in various applications. However, the power combiner required in such system adds to its complexity and detracts somewhat from its efficiency. Therefore, it is desirable, and it is an object of this invention, to provide a unique and novel arrangement for combining the output signals from the various separate RF amplifiers comprising the amplification system.
Proper and efficient operation of a particle beam accelerator requires that the resonant cavity of the accelerator be driven by a power amplification system which has the ability to have its output power dynamically controlled to compensate for beam dynamics, cavity temperature drifts, and RF droop. In typical klystron systems, this is accomplished by changing the RF drive level of the klystron and by the partial linear gain characteristics of the klystron tube. For either solid state or klystron amplifiers, a control range of about 10% is desirable.
In solid state amplifier systems for driving cavity resonators, control of the amplitude or power output of the amplification system cannot be conveniently accomplished by low level drive signal changes since the amplifiers typically operate under class C conditions. In order to alleviate this problem, the system shown in U.S. Pat. No. 4,064,464 may be used wherein the phase relationship between some of the amplifiers is changed for the purpose of changing the overall power output of the system.
Proper coupling of the outputs from separate amplifier systems requires the use of suitable isolators, directional couplers, or circulators. Since phase control does not change the amount of power supplied by a particular amplifier circuit or system, a change in coupling relative to the other amplifiers necessitates a loss or waste of power in the circulators, directional couplers, or isolators which are used to couple the systems together. Therefore, it is desirable, and it is another object of this invention, to provide a system for controlling or changing the power of an amplifier system driving a resonant cavity which does not waste or dissipate unneeded power in components used to combine the power from the separate amplifiers. The need for this advantage is particularly important in systems which are operating with extremely high power requirements.